ever make a franken-lens?

[tdeming]

So, I've got an old Zeiss protar series VII convertible with 2 equivalent approx 16" cells, as well as a Turner-Reich Triple Convertible with 21" and 28" cells that all fit into the threads of an old Ilex/Acme #4 shutter. Just playing around with these this weekend and tried mixing the T-R and Zeiss cells in different combinations. On the groundglass, the hybrid combos (for example, the 21" TR cell in back ,and a 16" Zeiss cell in front) seem to give images at focal lengths you would expect for the respective combinations, and the images appear (at least as well I can tell on the ground glass with a loupe) as sharp as the "correct" all zeiss or T-R pairs.

Has anyone else tried this? Aside from having to figure out the focal lengths and aperature scales for the different combinations, I'm wondering if there's any physical/math reason (for the lens gurus to contemplate) why these 4-element and 5-element cells cant be used in combination to give a sharp image that will cover 8x10? The spacings of the cells (originally from 2 different acme shutters) are identical via adapters on the cells, so the relative spacings of the front and rear elements to the shutter doesnt change in the combos, but I'm wondering if the lenses will be mismatched in some way. Otherwise, have I found a cheap way to a funky casket set? Looking for some advice before I try this out on film.

cheers

Tim

 

[athanasius80]

Do it for fun. It might work surprisingly well. I once found that a Paragon Anastigmat made a half decent fisheye lens with the front element missing.

 

[Ole]

Four- and fiveelement lenses will be reasonably well corrected, so using any two together should certainly not be worse than using any one alone...

You may find that there will be a little more distorsion if the shortest lens is in front of the shutter, though. That's one of the reasons why it's alays the front element that's to be removed when converting a Symmar or similar. Oh - and focal plane curvature too.